Embryogeny of Phaseolus: the Role of the Suspensor

Abstract

Summary Label 14 C-sucrose is administered to the developing embryos via the base of the excised pod, through the endosperm cavity of the seeds, and directly to the excised embryos. The results indicate that the suspensor is the uptake site during early stages of embryo development. When labeled solution is introduced into the endosperm cavity at the late heart stage of embryo development, radioactivity appears in the suspensor and the suspensor end of the embryo-proper. This labeling pattern is unexpected. One might have expected the cotyledonary half of the embryoproper to be more heavily labeled since it is nearer to the endosperm — the source of radioactivity. The uptake of 14 C-sucrose by the suspensor at the late heart stage is sensitive to dinitrophenol whereas the total radioactivity in the embryo-proper increases gradually with time and the uptake of 14 C-sucrose is not inhibited by the presence of dinitrophenol. The uptake pattern is changed at the mid-maturation stage. It appears that the cotyledons become the major uptake site for the maturing embryo. The results are discussed in relation to the current hypotheses of suspensor function.